Horton

Re: Patch: Write Amplification Reduction Method (WARM)

Bruce Momjian <bruce@momjian.us>

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From: Bruce Momjian <bruce@momjian.us>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Pavan Deolasee <pavan.deolasee@gmail.com>, Jaime Casanova <jaime.casanova@2ndquadrant.com>, Haribabu Kommi <kommi.haribabu@gmail.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2017-02-23T18:52:16Z
Lists: pgsql-hackers 
On Thu, Feb 23, 2017 at 03:45:24PM -0300, Alvaro Herrera wrote:
> Bruce Momjian wrote:
> 
> > Well, let's walk through this.  Let's suppose you have three updates
> > that stay on the same page and don't update any indexed columns --- that
> > would produce a HOT chain of four tuples.  If you then do an update that
> > changes an indexed column, prior to this patch, you get a normal update,
> > and more HOT updates can be added to this.  With WARM, we can join those
> > chains
> 
> With WARM, what happens is that the first three updates are HOT updates
> just like currently, and the fourth one is a WARM update.

Right.

> > and potentially trim the first HOT chain as those tuples become
> > invisible.
> 
> That can already happen even without WARM, no?

Uh, the point is that with WARM those four early tuples can be removed
via a prune, rather than requiring a VACUUM. Without WARM, the fourth
tuple can't be removed until the index is cleared by VACUUM.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +

Commits

  1. Implement SortSupport for macaddr data type

  2. Simplify check of modified attributes in heap_update

  3. Remove direct uses of ItemPointer.{ip_blkid,ip_posid}

  4. Fix CatalogTupleInsert/Update abstraction for case of shared indstate.

  5. Provide CatalogTupleDelete() as a wrapper around simple_heap_delete().

  6. Band-aid fix for incorrect use of view options as StdRdOptions.

  7. Update visibility map in the second phase of vacuum.

  8. Avoid having two copies of the HOT-chain search logic.

  9. Postgres95 1.01 Distribution - Virgin Sources